Because the Miata is the most popular track car there is, with NASA and SCCA class support and they're proven, cheap and plentiful. The BRZ looks promising, has a fixed roof and some smart engineering, but until they've been around for a decade or more, the Miata will continue to be the smarter track choice.

And here lays the problem... the Toyobaru has so, SO much potential and yet we ending up comparing it to the Miata performance wise. Why?!

Because the engine should have a fat torque curve without dips and peaks over the entire rpm range like the Renaultsport's engine (Renaultsport surely knows how to do a proper engine):